The minimum dimension that a given photolithography process can resolve is alternatively called the minimum feature-size or the critical dimension. The feature-size is a parameter of interest as reductions in the feature-size tend to improve speed performance of the IC. The feature-size of a printed integrated circuit (IC) is not uniform. The printing process results in slight variation of the feature-size from lot-to-lot, from wafer-to wafer, and from device to device within each wafer. As a result, programmable ICs, such as field programmable gate arrays (FPGAs) vary in static power and circuit delay due to variations in the manufacturing process. Slow devices usually have lower static power and fast devices usually have higher static power requirements.
As circuit designs continue to increase the speed and power efficiency requirements of target devices, it becomes increasingly important for developers to simulate and test circuit designs on target devices using precise power and delay specifications prior to realization. Many programmable IC vendors, such as Xilinx, Inc., measure switching speed of several printed devices of a product design to determine a minimum operating voltage and maximum delay that can be guaranteed to designers.
Due to variations from device to device, in order for the guaranteed specifications to apply to a majority of the printed devices, the guaranteed voltage and delay specifications are offset to include a certain amount of headroom. For example, measurements may indicate that the majority of product devices can operate on average at or above 110 megahertz (MHz) at 1V operating voltage but a small percentage of the devices will operate as low as 102 MHz at the same voltage. The specification may offset average speed of 110 by a headroom of 10 MHz to ensure devices perform as indicated in the specification. The presence of process variations degrade the performance and power specifications that manufactures can guarantee to customers. The larger the amount of variation, the larger the specification is offset by a headroom. Because of the included headroom, many printed devices in a product design are capable of performing with better voltage and delay parameters than that guaranteed in the vendor product specification.
One or more embodiments of the present invention may address one or more of the above issues.